The ability to reproducibly identify specific neuronal types has aided studies of the functional organization and development of the mammalian central nervous system (CNS). We have generated monoclonal antibodies that identify functionally distinct neurons in mammalian central visual areas. Monoclonal antibody Cat-301 identifies neurons in the dorsal lateral geniculate nucleus and striate and extra-striate cortex in cat, monkey and human. The distribution of Cat-301 positive neurons correlates with the functional organization of these areas. Further, we have demonstrated that the expression of the Cat-301 antigen during development requires normal visual experience early in life. These studies have shown that molecular differences among neurons correlate with their functional properties and that the phenotypic changes in neurons consequent to early experience are reflected by the expression of specific molecules. Here we propose to continue these studies to : 1. identify functionally related neurons in monkey visual cortex using monoclonal antibodies and correlative techniques; 2. map the cellular organization of human striate and extra-striate visual cortex; 3. use molecular markers to study experience-dependent neuronal development; and 4. biochemically characterize experience- regulated antigens. Our immediate goal is to further the description of the molecular substrates of the functional organization and development of central visual areas. Our long term goal is to use the conservation of antigens through evolution to extend these studies to the organization and development of the human visual system.